1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
Priority is claimed on Japanese Patent Application No. 2009-178907, filed Jul. 31, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
With high integration of semiconductor devices, there has been demand for a structure of a higher capacitance capacitor of a DRAM (Dynamic Random Access Memory) memory cell. For this reason, a cylindrical capacitor structure has been developed as a high capacitance capacitor.
With higher integration of semiconductor devices, an electrode of a cylindrical capacitor is made taller in order to increase a larger surface area thereof, and thereby achieve higher capacitance. However, the taller charge storage electrodes of the cylindrical capacitor lack physical stability, and therefore collapse during a manufacturing process, thereby causing a decrease in manufacturing yield.
To solve the above problem, Japanese Patent Laid-Open Publication No. 2008-283026 discloses a method of forming a supporter between adjacent cylindrical capacitors to prevent the cylindrical capacitor from collapsing. Specifically, the method includes the following processes (see FIGS. 4 (a) to 4 (d), 5 (a) to 5 (e), 6 (a), 8, and 10 of the above document).
Firstly, a capacitor inter-layer film and a support film are sequentially formed. A silicon oxide film and a silicon nitride film are used as the capacitor inter-layer film and the support film, respectively.
Then, a capacitor hole is formed so as to penetrate the support film and to extend into the capacitor inter-layer film. To maximally utilize the memory cell region for forming charge storage electrodes, adjacent capacitor holes are distanced from each other by approximately the minimum feature size of photolithography, and the diameter of the hole is set to be large. Consequently, charge storage electrodes are densely formed in the memory cell region, and the support films are formed in the other region.
Then, a charge storage electrode is formed so as to cover side and bottom surfaces of the capacitor hole. Then, a photoresist mask, which has an opening pattern for forming holes (called pouring holes) in the support film, is formed over the support film using photolithography. Since the charge storage electrodes are densely formed in the region of the support film, it is difficult to form the resist opening pattern so as to expose only an upper surface of the support film. For this reason, the resist opening pattern partially exposes upper surfaces of the support film and the charge storage electrode adjacent to the support film. An edge of the resist opening pattern overlaps the upper surface of the charge storage electrode in plane view.
In some cases, the pouring hole has been required to be increased in diameter in order to enhance circulation of an etching solution and a film forming gas, thereby exposing a larger area of the upper surfaces of the support film and the charge storage electrode (see paragraphs [0061] and [0065] of the above document).
Then, etching is carried out using the photoresist mask to remove a portion of the support film, which is exposed through the resist opening pattern and adjacent to the charge storage electrode, and thus to form the pouring hole. Consequently, a portion of the support film, which is not exposed by the resist opening pattern and therefore remains after the etching, mechanically supports the adjacent charge storage electrodes.
In this case, to surely form a connected portion of the charge storage electrode and the support film in the photolithography process, the photoresist mask has to overlap the charge storage electrode in plane view even if misalignment and a variation in size of the resist opening pattern occur. For this reason, the photoresist mask is designed so as to sufficiently overlap the charge storage electrode in plane view. For example, the photoresist mask is formed so as to cover approximately half the upper surface of the charge storage electrode (see FIGS. 6, 8, and 10 of the above document).
Then, an etching solution is introduced through the pouring hole, and the capacitor inter-layer film is selectively removed by etching so as to expose the outer side surface of the charge storage electrode.
Finally, a gas is provided through the pouring hole to form a capacitor insulating film and an upper electrode by CVD.
However, the inventor of the present invention found that the manufacturing method disclosed in the above document has the following problems.
In the process of forming the pouring hole in the support film by etching with the photoresist mask, high precision of the feature size is required, and therefore dry etching is used. By the dry etching, the support film is removed and the pouring hole is formed. At the same time, an upper portion of the charge storage electrode, which is not covered by the photoresist mask, is partially etched, and therefore a cutout portion is formed.
The cutout portion of the charge storage electrode includes a vertical etching surface and a horizontal surface. The vertical etching surface extends in a direction perpendicular to the substrate. The horizontal surface is in parallel to the substrate. An angled portion is formed at a point where the inner side surface of the charge storage electrode and the vertical etching surface are connected. The angled portion extends in the direction perpendicular to the substrate.
FIG. 19 is a cross-sectional view taken along a plan cutting the support film and illustrates the shape of the charge storage electrode including the angled portion. In this example, the opening pattern shown in FIG. 9 of the above document was used. As shown in FIG. 19, an angled portion 117B is formed at an angle of α degrees at the point where the vertical etching surface 117b and the inner side surface of the charge storage electrode 117 are connected.
The opening pattern is positioned so as to overlap the charge storage electrode 117 in plan view according to the mask design. However, the position of the edge of the opening pattern, which overlaps the charge storage electrode 117 in plan view, varies in a wafer surface due to misalignment and a variation in size of the opening pattern in the photolithography process. For this reason, a problem that the angle α varies from an acute angle to an obtuse angle arises. FIG. 19 illustrates a case where the charge storage electrode 117 has the angle α of approximately 50 degrees.
When a capacitor includes the charge storage electrode 117 including the angled portion 117B having an acute angle, the capacitor insulating film, and the upper electrode, the strength of the electric field acting on a portion of the capacity insulating film covering the angled portion increases, thereby causing an increase in leakage current. Consequently, an increase in consumption current of a device is likely to occur.